1. Field
Embodiments of the invention relate to the field of networking; and more specifically, to hierarchical virtual private LAN service (HVPLS) hub failure recovery.
2. Background
HVPLS (described in Internet Engineering Task Force (IETF) draft “draft-khandekar-ppvpn-hvpls-mpls-00”, dated November 2001) is an extension of Virtual Private LAN Service (VPLS) (described in Request For Comments (RFC) 4762 “Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling”, dated January 2007). VPLS allows networks at separate geographical locations to communicate with each other across a wide area network (WAN) as if they were directly attached to each other in a local area network (LAN). Customer Edge (CE) network elements, which are on the edge of geographically separate customer networks, are connected to Provider Edge (PE) network elements on an MPLS provider network. VPLS pseudowires (sometimes referred to as virtual circuits) are created and carried over Multiprotocol Label Switching (MPLS) tunnels. A pseudowire is configured for each pair of CE network elements that are to be connected into a virtual private LAN (i.e., for each CE that wishes to contact another CE). VPLS requires a full mesh of tunnels exist between all the PE network elements that participate in the VPLS service. To reduce the amount of signaling overhead and packet replication requirement of the full mesh, hierarchical connectivity (i.e., HVPLS) may be used.
An HVPLS network includes two tiers; a spoke tier and a hub tier. The spoke tier typically includes a multi-tenant unit (MTU) that is geographically located near the customer (i.e., customer network devices (e.g., switches, hubs, routers, bridges, computers, etc.) may be directly coupled with the MTU). The MTU is typically directly coupled with a PE network element over a single pseudowire (e.g., spoke pseudowire) for each VPLS service (e.g., a primary termination point for HVPLS spoke traffic). The MTU is not directly coupled with the other PE network elements in the HVPLS network. Thus, the MTU has a single point of connectivity to the hub. The hub tier includes the PE network elements which are coupled with a full mesh of pseudowires (i.e., hub pseudowires).
To protect against the spoke pseudowire failing or the primary termination point (e.g., the directly coupled PE network element) failing, the MTU may be dual-homed into two PE network elements. For example, for each pseudowire between the MTU and the directly coupled PE network element (referred to as primary pseudowires), a secondary pseudowire communicatively couples the MTU with a different PE network element (e.g., a secondary termination point for HVPLS spoke traffic). The MTU typically is able to detect a failure of the primary spoke pseudowire and/or failure of the primary termination point. Upon detecting the failure, the MTU may switch to the secondary spoke pseudowire and send HVPLS traffic to the second termination point.